Mechanical impact printers are known to the prior art for imprinting a succession of characters, which may be expressed in the form of a bar code or the like, on a succession of labels which removably adhere to an elongated strip of label stock backing. In such printers, the elongated strip is moved under tension along a predetermined path past a print station where the characters are successively imprinted. The print station may include a continuously rotating, cylindrical print wheel having located on a circumferential surface thereof a plurality of raised elements representing the characters to be imprinted, and a hammer mechanism including a hammer which has a selectively controllable, reciprocative movement in the predetermined plane whereby the hammer during its travel impacts the elongated strip and an interposed ink ribbon against one of the elements on the print wheel, resulting in imprinting of a single character.
To insure accurate and precise registration of successive characters on a label in a horizontal direction, or parallel to the predetermined path of label stock movement and to the direction of elongation thereof, the label stock backing must be vertically aligned with the print station including the aligned printed wheel and hammer mechanism. In the prior art, this alignment has been accomplished by the provision of a horizontal reference surface, which defines a plane extending at right angles to the plane of reciprocative movement of the hammer, against which the lower edge of the label stock backing bears during imprinting and label stock movement. It has been found, however, that the label stock backing will tend to rise or otherwise shift in a vertical direction from the horizontal reference surface during horizontal movement, with resulting misregistration of successive characters on a label. One solution to this problem would be the provision of a second horizontal reference surface for maintain the top surface of the label stock backing to maintain the vertical alignment thereof. However, the provision of such a second horizontal reference surface poses problems in that the label stock backing may often bind or be distorted during horizontal movement. In addition, the loading of label stock is made more difficult due to the necessity for inserting the label stock between the first and second horizontal reference surfaces.
It is therefore an object of this invention to provide an improved guide means for an impact printer which serves to maintain the vertical alignment of an elongated strip of print stock with respect to the vertical position of a print station including a hammer mechanism and a continuously rotating print wheel.
It is further object of this invention to provide such a guide means which does not bind or distort the print stock during movement past the print station.
It is yet a further object of this invention to provide such a guide means which is simple of construction and inexpensive of manufacture.